US President Donald Trump defended his daughter Ivanka Trump on Monday after she took his place at a meeting of G20 world leaders, an event that raised some eyebrows and drew sharp rebuke from the daughter of a rival former presidential candidate who was drawn into the fray.

"If Chelsea Clinton were asked to hold the seat for her mother, as her mother gave our country away, the Fake News would say CHELSEA FOR PRES!" he tweeted, referring to the daughter of Hillary Clinton, his Democratic rival in last year's presidential election.

Chelsea Clinton responded on Twitter: "Good morning Mr. President.
It would never have occurred to my mother or my father to ask me. Were you giving our country away? Hoping not."

White House adviser Ivanka Trump briefly sat in her father's chair on Saturday at a Group of 20 summit meeting in Hamburg, Germany, during a closed-door session on African development as the World Bank president spoke.

Her appearance prompted a string of reactions on Twitter and caught the attention of the German media and other outlets.

Donald Trump, in a separate tweet, called the arrangement "very standard" and also noted that German Chancellor Angela Merkel, who was hosting the G20 summit, agreed.

Merkel had dismissed the move at a news briefing after the summit.

"Ivanka belongs to the U.S. delegation," Merkel, who has worked with her on various issues, said last week.

Nikki Haley, the U.S. ambassador to the United Nations, also defended Ivanka, saying on Sunday that the president's daughter had often sat in on meetings with her and Trump, especially those regarding women and business.

Ivanka Trump ran a clothing and jewellery business before taking a formal job at the White House after her father took office in January and has adopted women's issues as a signature policy area.

At the G20, she also took the spotlight at a separate event alongside World Bank President Jim Yong Kim for a public-private loan programme aimed at boosting female entrepreneurs in developing countries.

Lawrence Summers, a former World Bank official and economic adviser under former Democratic president Barack Obama, said it was rare for government heads to leave during major summits and that, when they must, foreign ministers or other very senior government officials normally fill in.

"There is no precedent for a head of government's adult child taking a seat," he wrote in the Washington Post. "There is no precedent for good reason. It was insulting to the others present and sent a signal of disempowerment regarding senior government officials."